Frontal features of the Columbia River plume seen from a high-resolution non-hydrostatic model

Airborne data measured during the recent RIVET II field experiment has revealed that horizontally distributed thermal fingers regularly occur at the Mouth of Columbia River (MCR) during strong ebb tidal conditions. The non-hydrostatic coastal model, NHWAVE, was able to reproduce those features as the computational grid was refined to ~10 m. Model results indicate that large amplitude Kelvin-Helmholtz instabilities are generated in association with an internal hydraulic jump, which forms as the plume moves over bathymetric sills, and with location and orientation controlled by a lateral boundary inclined to the plume front. Simulation results indicate that the Kelvin-Helmholtz billows have sufficiently large amplitudes to interrupt the water surface, causing prominent linear features on the surface as indicated in thermal images. The current field in the interrupted region is modulated by the frontal structures, indicated by the vorticity field calculated from both the numerical model and data measured by the microASAR.